I have a bicycle frame that's really heavy. It's a mountain bike frame with shocks, so I decided to replace the entire frame with a city bike aluminum frame(I only use the bike if I have to pick up/buy some stuff near home). How do I know if the frame that I replaced is a titanium/steel?

I got the bike as a present from my uncle almost 6 years back, I don't have an idea about the brand, it's just the entire frame is not your average frame, it's somewhat heavier than other bikes( I compared it with the aluminum frame I bought/ plus a couple of my friends bike)

What methods/techniques should I use to know what type of frame do I have?

Use a magnet to see if it is steel. Titanium frames are rare and expensive, so this vector is unlikely.
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VoracNov 11 '13 at 10:53

2

Probably if it is much heavier, it's not the material so much as the design. Many walmart brands produce 30 or 40 pound creatures from what I assume to be very low grade steel (sometimes called "Mystery Pig Iron" alloy). A good steel frame can be more or less identical in weight to an aluminium one. Use the magnet.
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John DoucetteNov 11 '13 at 13:18

The shocks will give a good idea as to the value of the bike, as will the components such as derailleurs and brakes. Use that value to establish frame quality, from there, using a magnet, it should be easy to work out what its made of. My guess ("really heavy") is pig-iron.
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mattnzNov 11 '13 at 20:29

2 Answers
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To identify a frame firstly see if a magnet sticks, if it does it's steel, if not it's carbon, aluminium alloy or titanium alloy.

If not steel look down the seat tube if it's metallic inside it could be aliminium or titanium if black and plastic looking, carbon. Tap the frame with a screw driver, aluminium and titanium will have a definite metallic 'tink' and carbon a hollow 'thunk'.

To tell the difference between alloys put a small scratch in the seat tube (both have good anti-corrosion properties) if the exposed metal is dark and dull silver it's possibly titanium, if light silver it's aluminium. Titanium frames are expensive and rare so not likely to come across one you don't know the pedigree of.

For steel there is a significant difference between the two main types of steel, Chromoly and Hi-Ten steel. Chromoly is a stronger and lighter (high carbon) steel and is generally found on mid to high end bikes. If a bike is reasonably modern and chromoly it is likely to have smaller diameter tubes and possibly seat post (although this isn't a good indicator as new steel frames are being produced to fit dropper posts). A chromoly bike may have a sticker on the seat tube from the tube manufacturer be it Reynolds, Tange or Columbus. Tube shape may also vary on higher end frames (my chromoly HT has a triangle top tube and oval down tube). A Hi-Ten frame will mirror the fashion of when the bike was made.

Few Chromoly frames come as built up bikes so generally if you don't know your riding Chromoly, a magnet sticks to the bike and it's heavy you're riding a Hi-Ten steel bike. The scrap value of the frame is probably worth more than the frame.

"The scrap value of the frame is probably worth more than the frame." :)
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alexMar 14 '14 at 0:58

Did check it, found that it was really low quality steel. I have yet to use the aluminum frame, as I had to cover a lot of expenses fixing my car, so there are still some missing parts on the bike. But I am very eager to use it once I have completed its assembly.
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marchemikeMar 14 '14 at 3:19

Actually, there are usually quite easy ways to tell steel from aluminum. As one poster already mentioned, if it's pretty heavy, we can rule out titanium. This leaves us between steel and aluminum.

Generally, an aluminum bike will have larger tube diameters due to the properties of the material. On most steel bikes that I've seen, the seat tube is 28.6mm in diameter, while aluminum usually comes in at 31.8 or 34.9. Another heuristic that can be used quickly is the fact that *most* steel bikes use standard round tubes, while aluminum are more likely to be ovalized or shaped. Again, this is not true in all cases (see steel aero craze).

The sad state of affairs is that cheap department store bikes often have large tubes and are made of "steel". Presumably this is because the steel is such low grade that they require large tubes, or because the manufacturer thought it would make the bike "look cool". The result of this is that my kids have BMX style bikes with 16 inch wheels that close to as much as my old full size road bike which is also made of steel.
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KibbeeMar 13 '14 at 12:53